Discharge valve for granular material



May 15, 1962 D. STOUGHTON ETAL 3,

DISCHARGE VALVE FOR GRANULAR MATERIAL 2 Sheets-Sheet 1 Filed Oct. 14. 1958 12+ IOO FIG.I

INVENTORS SAMUELT. ROBINSON LINCOLN D. STOUGHTON y 15, 1962 D. STOUGHTON ETAL 3,034,689

DISCHARGE VALVE FOR GRANULAR MATERIAL 2. Sheets-Sheet 2' Filed Oct. 14. 1958 INVENTORS SAM T BINSON LlNCOLN S GHTON FIG. 3

6 m I ill/ 7407467167 7 F United States Patent I Ofiice The present invention relates to a valve and, more particularly, to a valve to control the discharge of spherical and other granular material.

Present Valves in use for the discharge of granular material generally rely on gates or flaps which place at least some of the material in shear or in compression upon closing. Where the size of the material varies, that is, where the material is a mixture of various sizes, this could and frequently does result in failure to achieve complete shut-oil due to blockage by the larger particles thereby permitting continued flow of the smaller particles. When attempts are made to achieve a complete shut-01f, some of the material is damaged by crushing or rupturing.

Such disadvantages of conventional type discharge valves are overcome by the present invention in which the use of shear or compression surfaces is totally avoided.

It is known that spherical granular material, unlike liquids, does not rise to seek its own level in interconnected passages, and advantage is taken of this fact in the design of this valve. Briefly described, the valve consists of a vertically disposed movable hollow tube or cylinder entering the bottom of a hopper from which the granular material is to be discharged. The bottom of the hopper is made to slope toward the cylinder so that when the top opening of the tube is dropped flush with the hopper bottom, the material will flow from the hopper through the tube into an external receptacle below. For purposes of permitting regulation of the How through the valve, the top of the tube is enclosed in a stationary hood of convenient shape having appropriate openings for permitting the granular material to flow into connection with the side of the tube. The openings in the side of the hood are at least as high as the diameter of the largest particle and preferably substantially larger, at least about two diameters, for best control. The interior roof of the hood is made high enough so that the top of tube can be placed above the top of the openings and thereby permit the flow of material into the tube to be terminated. It has been discovered that, as the tube is lowered, the spherical granular material will flow over the top of the tube at a rate approximately proportional to the distance between the top of the tube and the top of the openings in the side of the hood, thereby providing a method of varying the rate of flow of the granular material. As the tube is raised, flow will diminish and stop when the top of the tube reaches the same level as the top of the slots or openings in the hood periphery.

This invention, as will be hereinafter more particularly described, is particularly useful with a nuclear reactor of the type commonly known as a Pebble Bed Reactor, such as, for example, the one described in US. Patent No. 2,809,931, issued October 15, 1957, to F. Daniels and also the one to be hereinafter described, in order to avoid fuel element destruction which may occur, as already described, when a conventional flap or gate valve is used. Specific details of the theory and essential characteristics of a pebble bed reactor are set forth in the aforementioned US. patent.

It is, therefore, a first object of this invention to provide a simplified valve for use in the controlled discharge of spherical and other granular material.

It is a further object of this invention to provide a valve lacking shear or compression surfaces, being particularly Patented May 15, 1962 adaptable for use with the controlled, non-destructive discharge of granular material.

It is still another object of this invention to provide a valve particularly useful for the controlled, safe discharge of the solid fuel and blanket elements in a pebble bed nuclear reactor.

Other objects and advantages of this invention will hereinafter become more fully apparent in the light of the following description taken with the attached drawings wherein:

FIGURE 1 is an elevation view in section of a pebble bed nuclear reactor embodying the valve of this invention;

FIGURE 2 is a section along 22 of FIGURE 1;

FIGURE 3 is a section along 3-3 of FIGURE 1; and

FIGURE 4 is a detailed view of a portion of the interior of the reactor illustrated in FIGURE 1 without the presence of the blanket and fuel material to show a more detailed view of the inventive valve.

Referring to FIGURE 1, there is shown a valve 10 embodying the principles of this invention located within a pebble bed nuclear reactor 12. Valve 10 consists of a stationary hood member 14 and an axially slidable tubular member 16 with a top opening 17 and side opening 16a, opening 17 being for the discharge in the direction of arrow 'A of the granular fuel elements 18 and the blanket balls 20 located in reactor .12.

Reactor 12 comprises a pressure vessel 22 containing a reactive core 24, a thermal shield 25, a graphite grate 26 for supporting core 24, and other supporting structure to be later described. Pressure vessel 22 is made up of a bottom hemispherical section 27, a central tubular section 28 and a top hemispherical section 29, all of which may be welded together at the points indicated as 30. It is understood that pressel vessel 22 may be constructed in accordance with the ASME Code for unfired pressure vessels. A satisfactory vessel plate material is SA-212B steel with no special internal surface finish being required. The interior of vessel 22 is provided, as already noted, with a reactive core 24 surrounded by a thermal shield 25 of carbon steel having a shape generally cylindrical down to a point 33 just above the top of the bottom hemispherical section 27. From point 33 down to a baseplate 34, there is provided a frusto-conical shaped thermal shield section 36 which may be welded at its ends to shield 25 and base plate 34, respectively. Adjacent the top of vessel 22 a smaller thermal shield 38 supported by any convenient means from the top of section 29 is provided, leaving an annular opening 40 between shield 38 and the upper extension of shield 25 for the passage of coolant as will be later more particularly described. Thermal shield 25, along with section 36 and base plate 34 are supported by a pair of concentric core support tubes 42 and 44 extending from bottom vessel section 27 up to base plate 34 which rests thereon. Concentric tubes 42 and 44 are provided with a plurality of openings 52 and 54, respectively, to permit passage therethrough of the coolant. Base plate 34- is provided'with a central opening 56 for the passage therethrough of slidable tube 16 and also a plurality of three openings 58 located as illustrated for the entry therein of a coolant outlet tube 59. It will also be noted that bottom hemispherical section 27 of vessel 22 has a flanged opening 60 surrounding each gas outlet tube 59, leaving a concentric channel 61 for the entry of coolant, to be later described, the direction of flow indicated by arrows B and C.

Mounted on base plate 34 is a plate 62 of solid graphite and an upwardly extending cylindrical structure 64 also made of graphite having a plurality of openings 66 for the passage therethrough of the coolant. Graphite cylinder 64 assists in supporting graphite grate 26 which is of conical shape, pitched at some angle, such as 15, toward the centrally located discharge valve 10. As best seen in FIGURE 4, grate 26 is provided with a central opening 70' in which the stationary hood unit 14 of valve is located. Hood unit 14 is provided with a lower cylindrical section 72 extending down from the top of of grate 26 to the top surface of base plate 34 where hood 14 rests thereon. A plurality of six conveniently shaped openings 74 extending from the top of grate 26 upwardly is provided in hood 14 for the entry of the spherical granular material. Top opening 17 of tube 16 is shown in FIGURE 1 at a position adjacent the top of openings 74, and at this point in the upward movement of tube 16, for example, the solid material will cease to flow. Also, the radial distance between the outer top edge of tube 16 and the tops of openings 74 should be greater than the diameter of the largest particle to prevent jamming. Below this point the material will flow into top opening 17 of tube 16. Between cylindrical section 72 and tube 16, there is provided a cylinder 76 of graphite to take up the space. An outer graphite cylinder 77 supports grate 26 centrally.

As more particularly shown in FIGURE 3, grate 26 consists of a plurality of twelve wedge-shaped segments 79 having a pair of end members 80 radially extending and a plurality of spaced parallel arms 81 for permitting flow therethrough of the coolant gas and at the same time supporting the fuel and reflector balls 18' and 29, respectively.

Supported on grate 26 are a plurality of s'm graphite cylinders 82 which are each bored axially with an oblate hole forming fuel chambers 83. The outside of each cylinder 82 is machined flat on three adjacent sides, as illustrated in FIGURE 2, so that these six cylinders can be nested together to form a central, hexagonal-shaped chamber 90. Adjacent cylinders 82 may be keyed together by convenient means (not shown) so as to form an integral structure of graphite. Each cylinder 82 is provided with a pair of longitudinal holes 92 for cylindrical control rods 94, shown in FIGURE 1. As is understood in the art, control rods 94 are provided as a means of controlling the reaction and are made of material such as cadmium or boron having high neutron absorption. Any convenient means (not shown) may be used for the controlled movement of rods 94, such as that illustrated and described in US. Patent No. 2,841,018. It will also be seen that core 24 forms an annular space or blanket chamber 94 for blanket material balls 20. Through the longitudinal walls of cylinders 82, adjacent grate 26, are provided several approximately rectangularshaped openings 96 and 97 to form passageways between adjacent cylinders 82 and between the central fuel chamber 90 and the outer fuel chambers 83, respectively, and thereby between the interior of core 24 and blanket chamber 94, as best shown in FIGURE 2.

Topping outer cylinders 82 and central chamber 90 there are a plurality of convergent-divergent, nozzleshaped cylinders 10% for the outer chambers 83 and 102 for the central chamber 90. For each of cylinders 100 and 102, there is a closure 104 and 106, respectively, made of solid graphite. Each of closures 104 and 106 is supported by rods 108 and 110, respectively, which are made hollow to permit fuel to be loaded therethrough as well as to support the closures 104 and 106. In addition, six hollow blanket loading tubes 112 are mounted vertically through top vessel section 29 over blanket chamber 94 and arranged equally spaced in a ring to permit blanket balls 21 to be loaded into annular chamber 94. The graphite material making up the walls of the fuel chambers 83 and 90, grate 26 and closures 104 and 106 provide reflection for the neutron flux as is understood in the art. For the capture of neutrons which es cape the graphite material enclosing reactive core 24, blanket chamber 94 is filled with blanket balls containing a non-fissionable isotope, such as thorium (90 in (it thorium oxide to produce the fissionable isotope U as is now understood in the art. A more detailed description of the fuel and blanket balls will appear later.

The coolant selected for use in reactor 12 to carry away the heat developed therein for use in a steam power plant, such as one described in the aforementioned US. Patent No. 2,809,931, is helium. Helium is a gas which is totally inert and does not absorb neutrons, and furthermore, it is the only gas having a good pumping power/ heat transfer modulus that will not react with the core materials.

The flow of helium through reactor 12 is as follows: Under pressure, the helium enters the bottom of vessel 22, through the annular space 61 between the outlet tubes 59 and flanges 60, as indicated by arrows B, and passes through openings 54 and 52 in core support cylinders 44 and 42, and then up through the annular space between thermal shield 25 and pressure vessel 22, comprising the first pass of the reactor. The helium then enters the main chamber of vessel 22, through the annular opening 40 formed between thermal shields 25 and 38, and flows down through the interstices between the blanket balls and the fuel balls. The helium flows down through all the fuel chambers 83 and 90, as Well as annular blanket chamber 94, then through the openings in grate 26, openings 66 in support core cylinder 64, and then out of vessel 22 through the gas outlet tubes 59 as indicated by arrows C. It will be seen that some of the incoming helium will enter valve tube 16 through openings 16a so that a portion of the pressurized helium will pass directly from annular passageway 61, through openings 16a into tube 16, into the interior portion of hood 14, out through openings 74 in hood 14, and rejoining the main flow of helium passing down through grate structure 26.

It will be seen that the design of reactor 12 is such as to make unloading of the fuel and blanket balls through valve 10 and reloading of the balls through tubes 108, 110 and 112 possible without dismantling any of the vessel internals.

To utilize valve 10 to unload core 24 and blanket chamber 94, tube 16 is lowered to bring the top opening 17 thereof below the top of openings 74 as previously described. Tube 16 may be actuated by a canned motor drive (not shown), external to the reactor, similar to those used for control rod drives, such as illustrated in US. Patent No. 2,856,336. Control of the flow of balls through valve 10 is based upon the fiow characteristics of spherical particles. Unrestrained, they have a zero angle of repose, i.e., they behave like liquids. However, unlike liquids, they cannot rise to seek their own level in interconnected regions. That is, they will not rise above the level of the opening through which they are flowing. Thus, when the top opening 17 of tube 16 is at some point below the top of openings 74, the balls will flow over the top and down through tube 16. When tube 16 is raised above this point, the former will act as an abutment, and flow will be stopped without the possibility of catching or jamming, thereby destroying, any of the balls. Chamber 90, including the blanket balls directly on grate 26, is the first chamber to be emptied. Then the outer fuel chambers 83, followed by the blanket balls directly underneath, are next emptied, and finally the blanket balls in blanket chamber 94.

To load reactor 12, blanket balls 20 are first loaded through hollow tubes 112 into blanket chamber 94 until the balls fill up chamber 94 to the level indicated in FIG- URE 1. It is understood from the discussion immediately above that blanket balls 20 will pass through openings 96 and 97 in the graphite cylinders 82 and form a blanket of balls parallel with the top of grate 26, reaching to the tops of openings 96 and 97 and the tops of hood openings 74 and filling the interior of hood 14 to top opening 17 of tube 16, as shown. Then fuel balls 18 are loaded into reactor 12 through fuel loading tubes 108 and 110, filling Table I Diameter, in 1% Number required 228, 600 2, 370,000 Graphite density, gmJcc. 1.

Composition UOz-l-ThO: Th; Oxide loading, wt. perce 10 50 U02 loading, grns 0.449 Th0; loading, gms 4. 94 5.66

One way to manufacture these balls is to impregnate preheated spheres (150 C.) of graphite in a boiling uranyl nitrate solution, air dry the spheres, bake at 275 C. to drive off N0 and finally bake at about 800 C. in a helium atmosphere. When graphite is impregnated with uranyl nitrate in this manner, the uranium is present as U0 In a fuel element which is to contain both thoria and urania, the impregnating solution could contain thorium nitrate and uranium nitrate in the proper portions. The loading required in a 125 eMW-PBR, for example, is 10% by weight of U0 and T1102. If, under some circumstances, it is desirable to have more than about 10 wt. percent total oxide, the Th0 could be added at the time the ball was molded (using unirradiated thoria, which would present no material handling problems) and the uranium added later by impregnation.

Principal characteristics of a 125 eMW-PBR, such as described above, are given in Table II as follows:

Table II Pressure vessel Design pressure 1100 p.s.i, Design temperature 650 F. Test pressure 1650 p.s.i.

Prevailing ambient. iqSlgIQlil-UPV Code (1956).

Test temperature Code requirements Inside diameter Overall length 21'0". Cylindrical wall thickness-" Hemispherical head thickness 2 y 1 ,000 lbs Weight, empt 2 'lherma shield thickness 1- 2".

Nuclear:

Core C/Th/U atom ratio 3745/11/1.

Blanket C/Th atom ratio 22/1.

Critical mass (1200 F., Eq.

Xe), kg. U-233 U-233 loading, kg Th-232 loading in core, kg 992.2. 'lh-232 loading in blanket, kg 11,780. Fuel burnup rate, kg/MW year- 0.48.

Initial capture to fission ratio 0.257. Fraction of epithermal fissions- 0.372. Inlti%l breeding ratio:

Average IBR over core lifetime- Average power density, watts/ 0.863.

cc 23.7 Atom burnup (percent total atoms) Core (after 100 days). 0.021.

Blanket (after 1500 days) Temperature coetficient Initial multiplication facto Kat! (1200 F., Eq.X

Kat! (1200 F., E%Xe) 1.070.

Kati (77 F., No Average thermal flux at start- Reactivity worth, initial 17.3%.

Thermal and fluid dynamic characteristics Design power level, MW 350. Design pressure level, p.s.i.a 1000. Design helium flow, lbs./hr 1,360,000. Volumetric heat generation,

MW/ft. core .683. .Volumetric heat generation,

MW/ft. ball bed .915. Temperature, F.:

Reactor inlet 550. Reactor outlet 1250.

Core outlet, avg 1540. Blanket outlet, avg 658. Fuel element surface, max- 2170. Fuel element center, max..- 2440. Operating power level, MW 337. 7 Core contribution MW 291.5.

Blanket contribution MW 45.5. Operating pressure level,

p.s. .a 965. Operating helium flow, lbs/hr-.. 1,343,000. Core pressure drop, p.s.i 15.5.

1 Equivalent bare homogenized core model. Heterogeneous multiregion with equilibrium blanket compositron.

At equilibrium conditions. after 10 core lifetimes.

It is thus seen that the valve hereinabove described permits the discharge of the spherical granular material without the possibility of damaging or destroying any of the individual balls because there are no gates or flaps or other closure members which could do this. In addition, the valve as described permits, by a very simple arrangement, the control over the rate of discharge over the balls. Furthermore, the valve, while embodying all of the advantages and benefits hereinbefore made evident, is simple in construction and operation and does not rely on fine tolerances of construction.

While the valve has been described in connection with the discharge of spherical elements, or balls, of particular materials, it is understood that a valve built according to the principles of this invention could function with any granuluar material having the suitable flow characteristics previously enumerated. Also the balls could be made from, for example, other types of materials, or granular material made up of less than spherical elements having the aforementioned fiow characteristics.

Concerning the construction of the valve itself, it is obvious that many modifications and variations in the construction thereof are possible in the light of the above teachings and that, therefore, the invention may be practiced otherwise than as specifically described within the scope of the appended claims.

We claim:

1. A dispenser for the regulation of gravity-fed, granular material of spherical particles of a predetermined maximum size comprising, in combination, a hopper with an opening at the apex thereof, a vertically extending hollow member open at the top thereof extending into said hopper through said opening for discharging said material contained in said hopper, means to limit the upward movement of said hollow member, and a hooded member mounted in said hopper covering both said opening and the top of said hollow member provided with a vertically extending wall having at least one side opening for permitting entry of said material into the interior of said hooded member and said hollow member through the open top thereof, the walls of said hollow and hooded members being substantially parallel and spaced from each other a sufficient distance to prevent jamming of said material between said members, said hollow member being axially movable to permit j am-free regulation of How through said valve in accordance with the vertical distance from the open top of said hollow member to the top of said side opening, the limit of the upward movement of said hollow member being with the top edge thereof spaced from said hooded member at a distance greater than the diameter of the largest particle in said granular material to prevent jamming and damaging of said material and means for axially moving said hollow member.

2. A dispenser for the safe discharge of spherical fuel elements from the interior of a gas cooled pebble bed nuclear reactor, comprising, in combination, a conically shaped grate for passing said gas through said reactor and supporting said fuel elements, said grate having a central opening and a vertically extending hollow member open at the top extending into said [grate through said opening for controllably discharging said fuel elements contained in said grate, and a hooded member mounted on said grate for covering said opening and the top of said hollow member, said hooded member provided with a vertically extending side wall having at least one side opening for permitting entry of said elements into said hooded member and said hollow member through the open top thereof, the walls of said hollow and hooded members being substantially parallel and spaced from each other a distance greater than the largest size fuel element to prevent jamming of said material between said members, and said hollow member being vertically movable to permit jam-free regulation of flow through said valve in accordance with the vertical distance from the open top of said hollow member to the top of said side opening, and means for vertically moving said hollow member.

3. A dispenser for controlling the gravitational feed of granular material of spherical particles of a predetermined maximum size without damage thereto comprising, in combination, a container for said material having a downwardly sloping bottom wall, a discharge opening at the lowermost portion of the bottom wall, stationary means, super-adjacent said discharge opening for blocking flow of said granular material through said opening said stationary means having a side wall with at least one opening through which said granular material will flow by gravity, movable abutment means between the side wall and said discharge opening spaced from the side wall a distance greater than the largest size particle in said granular material movable between positions completely blocking, partially blocking and completely unblocking the flow of granular material through the discharge opening, the completely blocking and unblocking positions being where the top of the hollow member is a predetermined distance above and level with the plane of the discharge opening respectively, and means for vertically moving said movable abutment means between said positions thereby regulating the flow of said granular material without jamming of said material.

References Cited in the file of this patent UNITED STATES PATENTS 1,111,230 OMeara Sept. 22, 1914 1,144,259 Steel June 22, 1915 1,147,325 Johnson July 20, 1915 1,224,822 Williams May 1, 1917 2,381,319 Swift Aug. 7, 1945 2,809,931 Daniels Oct. 15, 1957 2,811,285 Stasny Oct. 29, 1957 2,812,303 Daniels Nov. 5, 1957 

